An excellent discussion by Ibn Abū al-ʿIzz al-Ḥanafī concerning the outcomes and branches of such a pantheistic belief. He also shows which sects from amongst Islām have unfortunately adopted this evil creed.

Traveling with the intention of visiting the grave of the Prophet is bidʿah and is ḥarām, because of the ḥadīth which forbids traveling to worship in any place except the three mosques. As for visiting the grave of the Prophet (peace and blessings of Allāh be upon him) when one happens to be in Madīnah, this is perfectly acceptable, as is traveling with the intention of praying in the Prophet's Mosque as an act of worship and seeking to draw close to Allāh. Those that are confused about this issue are those who do not understand the difference between what is permitted and what is forbidden.